The Medical Breast Cancer Section is responsible for the development of a clinical and laboratory program directed at breast cancer. Clinical trials in metastatic disease comparing chemotherapeutic, hormonal and chemohormonal regimens are underway. Biochemical and hormonal receptor studies are undertaken and coordinated by the Medical Breast Cancer Section. Clinical studies consist of a major chemotherapy trial aimed at stimulating human breast cancer cells with hormonal agents for more successful cell cycle phase specific chemotherapy; a hormonal therapy trial aimed at prospectively evaluating the usefulness of complete endocrine ablation in human breast cancer. Concurrent cytokinetic data are being collected. Phase II trials of CBDCA and leukovorin followed by 5-Fu are underway. We have developed a successful treatment program for Stage III breast cancer (objective response rate 94%) (51% CR rate). We are attempting to further refine these techniques. We have initiated a randomized trial to explore the usefulness of an in vitro chemosensitivity assay system in collaboration with Helene Smith, Ph.D. (Peralta Cancer Research Institute). A trial for Stage IV no evidence of disease patients continues. In addition there is an endocrine and chemotherapy program for male breast cancer. A cooperative trial between the Surgery, Radiation and Medicine Branches is underway comparing excisional biopsy plus definitive radiotherapy to simple mastectomy in clinical Stage I and II breast cancer. All patients have axillary dissections; A-C chemotherapy is given to all N+ patients; 232 patients are on study.